Most consumers agree that the corrosion of glassware from use of detergent compositions in automatic dishwashing (ADW) is one of their most serious unmet needs. The current consensus amongst manufacturers is that the glassware corrosion problem occurs during the washing cycle of an automatic dishwashing appliance and may be the result of two separate phenomena acting-silica hydrolysis and metal ion leaching. Iridescence and clouding of glassware surfaces result when dissolved silica/silicate in combination with other silicate (added to prevent china and metal corrosion) deposit on glassware surfaces in high pH ADW environments. This phenomenon is known as silica hydrolysis. Glassware surface damage also results when chelate/metal ions on the glassware surface are removed during the wash cycle by the presence of a builder in the wash liquor. The removal of chelate/metal ions causes the surface to become less durable and less chemically resistant. This phenomenon is known as metal ion leaching. After several wash cycles in an ADW appliance, both phenomena can cause visible, unwanted damage to glassware in the form of cloudiness, abrasions, scratches, and streaks.
Although some manufacturers have tried to overcome these problems with the inclusion of corrosion protection agents in their ADW detergent compositions, the use of corrosion protection agents (such as, insoluble metal ions) may result in a number of manufacturing drawbacks. These include: (a) an increased cost of manufacture; (b) the need for higher salt level formulations; (c) the thinning of gel detergent compositions by metal ion interactions with thickener materials; and (d) the reduction of cleaning performance for certain stains (e.g. tea) generated by negative interactions of the metal ions with bleach during the wash cycle.
Although some ADW detergent compositions containing metal ions and low levels of nonionic surfactants are known, the levels of these nonionic surfactants have been limited to less than 8% by weight of the composition. This is due in part to the limited solubility of the nonionic surfactants in the wash solution. Therefore, the need continues for an ADW detergent composition that provides both glassware corrosion protection benefits and good cleaning benefits associated with higher levels of low-foaming nonionic surfactants, without unacceptable solubility negatives.